A femto BS is a small-size version of the macro BS which performs most of the functions of the macro BS and which may be installed in a region covered by the macro BS or installed in a dead zone which is not covered by the macro BS. femto BSs have an independently-operated network architecture and a much greater number of femto BSs than relay base stations may be installed downtown or indoors.
FIG. 1 illustrates the configuration of a wireless communication system having femto Base Stations (BSs).
Referring to FIG. 1, the wireless communication system may include a femto BS 110, a macro BS, a Femto Network Gateway (FNG) 130, an Access Service Network (ASN) 140, and a Connectivity Service Network (CSN) 150. The macro BS is a legacy BS in a conventional wireless communication system.
It is assumed that the femto BS 110 directly accesses a Transmission Control Protocol/Internet Protocol (TCP/IP) network and independently operates like the macro BS and the femto BS 110 covers 0.1 m to 30 m and may serve 10 to 20 MSs. The femto BS 110 may operate in the same frequency as the macro BS (in the case of intra FA) or a different frequency from the macro BS (in the case of inter FA).
The femto BS 110 is connected to the macro BS via an R1 interface for receiving a downlink channel from the macro BS and transmitting a control signal to the macro BS.
The femto BS 110 may cover an indoor area or a shadowing area that the macro BS cannot cover, and may also support high-rate data transmission. The femto BS 110 may be overlaid on a macro cell or installed non-overlaid in an area that the macro BS does not cover.
There are two types of femto BSs, Closed Subscriber Group (CSG) femto BSs and Open Subscriber Group (OSG) femto BSs. The CSG femto BS groups MSs that can access the CSG femto BS and assigns a CSG Identification (ID) to the group of MSs. Hence, the CSG femto BS may discriminate MSs having the CSG ID against MSs having no CSG ID when they access the CSG femto BS. On the other hand, all MSs can access the OSG femto BS.
The FNG 130, which is a gateway for controlling the femto BS 110, is connected to the ASN 140 and the CSN 150 via an Rx interface and an Ry interface, respectively. The femto BS 110 may receive a service from the CSN 150 through the FNG 130. A Mobile Station (MS) connected to the femto BS 110 may receive services such as authentication, Internet protocol Multimedia Subsystem (IMS) service, etc., from the FNG 130 or the CSN 150.
The CSN 150 may provide connectivity to an application service such as the Internet, Voice over IP (VoIP), etc, and provide authentication and billing functions to the MS. The ASN 140 may control the macro BS and manage a connection between the macro BS and the CSN 150.
The CSG type femto BSs may be classified into two types according to accessibility by non-member AMSs, i.e., AMSs having no CSG ID.
The CSG-closed femto BS (or ABS) is a type of femto ABS which allow access only by member AMSs. An AMS may store CSG-closed femto ABSs IDs, which permit access by the AMS, in a white list.
On the other hand, the CSG-open femto BS (or ABS) is a type of femto ABS that preferentially supports services for member AMSs and also permits access by non-member AMSs when resources are sufficient. However, the CSG-open femto ABS may differentiate the service level for member AMSs from the service level for non-member AMSs.
In the current mobile communication system using femto ABSs, it is assumed that the two CSG type femto ABSs, which are classified according to accessibility by non-member AMSs as described above, are fixed. CSG-open/closed femto ABSs can be discriminated through partition information in an Advanced Air Interface System Configuration Descriptor (AAI_SCD).
On the other hand, in the case where macro and femto ABSs are installed in the same frequency region, non-member CSG AMSs connected to the macro ABS may undergo interference from neighboring femto ABSs. In this case, the macro ABS may control interference to AMSs by preventing the femto ABSs from using a specific resource region.